A high ratio of dietary animal to vegetable protein increases the rate of bone loss and the risk of fracture in postmenopausal women

Background: Different sources of dietary protein may have different effects on bone metabolism. Animal foods provide predominantly acid precursors, wh ereas protein in vegetable foods is accompanied by base precursors not foun d in animal foods. Imbalance between dietary acid and base precursors leads to a chronic net dietary acid load that may have adverse consequences on b one. Objective: We wanted to test the hypothesis that a high dietary ratio of an imal to vegetable foods, quantified by protein content, increases bone loss and the risk of fracture. Design: This was a prospective cohort study with a mean (+/-SD) of 7.0 +/- 1.5 y of follow-up of 1035 community-dwelling white women aged >65 y. Prote in intake was measured by using a food-frequency questionnaire and bone min eral density was measured by dual-energy X-ray absorptiometry. Results: Bone mineral density was not significantly associated with the rat io of animal to vegetable protein intake. Women with a high ratio had a hig her rate of bone loss at the femoral neck than did those with a low ratio ( P = 0.02) and a greater risk of hip fracture (relative risk = 3.7, P = 0.04 ). These associations were unaffected by adjustment for age, weight, estrog en use, tobacco use, exercise, total calcium intake, and total protein inta ke. Conclusions: Elderly women with a high dietary ratio of animal to vegetable protein intake have more rapid femoral neck bone loss and a greater risk o f hip fracture than do those with a low ratio. This suggests that an increa se in vegetable protein intake and a decrease in animal protein intake may decrease bone loss and the risk of hip fracture. This possibility should be confirmed in other prospective studies and tested in a randomized trial.